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From: Gareth
Newsgroups: sci.electronics.design
Subject: Re: Interesting problem to solve
Date: Sat, 19 Oct 2002 11:28:45 +0100
Message-ID: <3DB133DD.3090904@nobody.nowhere.invalid>
References: <3DAFBB9D.58C1F0BB@scazon.com> <3DAFF518.2F4DBF7B@juno.com>
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Brill Pappin wrote:
> Actually, when I started thinking about this, I was thinking of how your
> ears hear sound, as a delayed sign wave (the sound) as it hits first one
> ear, then the other.
> I didn't mention it until now because that not really what I'm pondering,
> only what got me to thinking in the first place.
>
> - Brill Pappin
>
> "mike" wrote in message
> news:3DAFF518.2F4DBF7B@juno.com...
>
>>I'm gonna go out on a limb here and state that if the signals are
>
> sinusoidal
>
>>and continuous, you have no way to determine whether they are delayed
>>or out of phase by more than one cycle...unless you have additional
>
> unstated
>
>>information available.
>>
>>mike
Brill,
Mike is correct, the measurement is ambiguous unless you add other
information, such as pulsing the sine wave or sweeping the frequency.
This is similar to a problem in radar known as ambiguous range. The
radar transmits a signal (usually a pulse) and waits for an echo, but,
in the simple case, there is know way of knowing which of the previous
pulses actually caused the echo. There are a few solutions to this
problem such as changing the pulse repetition frequency.
Our ears cannot tell if a pure sine wave is delayed by more than one
cycle or not. Most sounds, such as music or speech, are not a single
tone and so contain many different sine waves. These sounds are not
continious and do not repeat exactly in a short period of time. The
ambiguity can therefore be resolved.
The wavelength of sound at 1KHz is about 1 foot, i.e. more than the
distance between your ears, so for many sounds the delay cannot possibly
be more than one period.
It is very difficult to locate the source of a high frequency single
tone sine wave. I read of some experimental siren for emergency
vehicles where a pulse of broadband white noise was added to the sound
of the siren at regular intervals. The white noise helped other drivers
to locate the emergency vehicle much more quickly than they were able to
do with a normal siren.
Gareth.
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